Cyclically operable optical shutter

ABSTRACT

A cyclically operable, optical shutter particularly suited for use as a focal plane shutter, characterized by an occulting disk having a pair of radiation occulting sectors defining therebetween a pair of diametrically opposed, radiation transmitting sectors driven in rotation by a D.C. motor. A particular feature of the shutter resides in a combination of a servo-control system with the motor for accelerating the disk from a steady state of zero velocity to a preselected steady state of angular velocity, maintaining the steady state during a predetermined period of radiation transmission, and subsequently decelerating the disk to a steady state of zero velocity within a fraction of a single revolution, whereby a pulse of radiation having a preselected width is gated through an associated aperture with a high degree of uniformity and reproducibility.

United States Patent Low et al.

1541 CYCLICALLY OPERABLE OPTICAL SHUTTER 22 Filed: Oct. 15,1970

21 Appl. No.2 81,096

-[ 7 3,704,659 [451 -Dec.5,fl1972 622,955 4/1899 Kelley ..95/59 PrimaryExaminer-John M. Horan Attorney-John R. Manning, J. H. Warden and MonteF. Mott [s71 ABSTRACT A cyclically operable, optical shutterparticularly suited for use as a focal plane shutter, characterized byan occultingdisk having a pair of radiation occulting sectorsdefiningtherebetween a pair of diametrically opposed, radiationtransmitting sectors driven in rotation by a DC. motor. A particularfeature of the shutter resides in a combination of a servo-controlsystem with the motor for accelerating the disk from a steady state ofzero velocity to a preselected steady state of angular velocity,maintaining the steady state during a predetermined period of radiationtransmission, and subsequently decelerating the disk to a steady stateof zero velocity within a fraction of a single revolution, whereby apulse of radiation having a preselected width is gated through anassociated aperture with a high degree of uniformity andreproducibility.

8 Claims, 11 Drawing Figures [52] [1.8. CI. ..95/59, 95/l2.5, 352/169[51] Int. Cl. ..G03b 9/10 [58] Field of Search ..95/59, 61, 11; 352/169[56] References Cited UNITED STATES PATENTS 2,937,583 5/1960 Redficld..95/11 3,106,126 10/1963 Kirk ....352/l69 3,178,721 4/1965 Kamp....352/169 3,603,678 9/1971 Anderl et a1... ....352/l69 2,383,3818/1945 Hammond ..95/61 2,350,355 6/1944 Hoffmann v.95/61 l RAMP IGENERATOR PATENTEDUEC 5 I972 SHEET 2 0F 4 EDWIN E DOB/ES IN VE N TOR ATTO/PNEYS CYCLICALLY OPERABLE OPTICAL SHUTTER ORIGIN OF INVENTION Theinvention described herein was made in the performance of work under aNASA contract and is subject to the provisions of Section 305 of theNational Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat.435; 42 U.S.C. 2457). 4

BACKGROUND OF THE INVENTION a l. Field of the Invention The inventionrelates to operable shutters and more particularly to an optical shutterfor use in photographic operations wherein accurate light gating isrequired in transmitting pulsed radiation through relatively largeapertures with a high degree of operational predictability and lighttransmission uniformity.

2. Description of Prior Art 7 (The prior art is replete with opticalshutters for use with cameras employed in conventional photography.Normally focal plane shutters are restricted to a 70 millimeter format,or smaller, while larger formats employ aperture plane shuttering. Lunarand planetary photometric photographygenerated a need for camerashutters having uniformity of exposure of better than one percent over afield of not less than 3 inches in diameter on a 4 inch by inchphotographic plate with exposure periods selectable over a wide rangeextending from approximately 2 milliseconds to periods of 32 seconds andmore. Any shutter employed must function with a high degree ofreproducibility and accuracy in cycle control.

Spring and solenoid driven shutters generally are suitable for use wherea light transmitting aperture is small and/or a relatively long timeinterval is utilized in conducting a given photographic operation.However, where a camerasimultaneously utilizes a large aperture andrequires a'variable, relatively narrow pulse of light, difficulty inacquiring pulse reproducibility, system predictability and transmissionuniformity has heretofore plagueddesigners of optical shutters.

OBJECTS AND SUMMARY OF THE INVENTION Therefore, it-is an object of theinstant invention to provide an improved shutter for effectively gatingradiation.

Another object is to provide an improved optical shutter includingimproved shutter components interrelated within a system havingparticular utility in enhancing photographic operations conducted withcameras having relatively large fields in environments requiring a widerange of selectivity in exposure intervals.

It is another object of the instant invention to provide aservo-controlled optical shutter for accurately providing uniformlygated light pulses with a high degree of pulse uniformity andreproducibility.

It is another object of the instant invention to provide aservo-controlled optical shutter which accommodates a preciseutilization of large quantities of power in achieving uniformity oftransmission of relatively narrow pulses of light through largeapertures over a wide range of exposure intervals.

It is another object of. the instant invention to provide aservo-controlled optical shutter including an occultingdisk whichcyclically transmits a single pulse of radiation through large aperturesfor cyclically establishing a single pulse of selectable duration withina fraction of a single revolution of rotation of the disk.

It is another object of the instant invention to provide an improvedoptical shutter which utilizes an occulting disk driven in rotationwhile effects of reaction torque are precluded by an application of areversely directed reaction torque of a similar magnitude.

These and other objects and advantages of the instant invention areachieved by providing an aperture adjacent an occulting disk having apair of diametrically opposed light transmitting sectors of differingdimensions driven by a servo-controlled system at selectively variable.accelerating, steady state, and decelerating angular rates all within afractional turn of a single revolution, whereby an accurate and uniformgating-of pulsed light through large apertures is accommodated over awide range of transmission intervals.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of ashutter which embodies the principles of the present invention.

FIG. 2 is an end elevation of the shutter of FIG. 1.

FIG. 3 is an enlarged, partially sectioned side elevation takengenerally along line 33 of FIG. 2.

FIGS. 4a through 4d together comprise an illustration of an operativesequence for the shutter shown in FIGS. 1 through 3.

FIG. 5 is a view schematically illustrating the shutter of FIGS. 1through 3.

FIG. 6 is a diagrammatic view illustrating stabilizing forces developedthrough an application of reaction torque acquired from a counter rotoremployed in stabilizing the shutter against reaction torque inducedrotation.

FIG. 7 is adiagrammatic view illustrating a given control signalobtainable from the ramp generator of FIGS, as the generator is drivenin a first mode of operation.

FIG. -8 is a diagrammatic view illustrating an alternate form of asignal which may be obtained from the ramp generator of FIG. 5, as it isdriven in a second mode of operation for imposing on the shutter astepping function.

DESCRIPTION OF THE PREFERRED EMBODIMENT General Description Referringnow to the drawings wherein like reference characters designate like orcorresponding parts throughout the several views, there is shown in FIG.I a shutter 10 which embodies the principles of the instant invention.

The shutter 10 includes an aperture plate 12 having a circular aperture14 extended therethrough with its optical axis, not designated,extending normal to the plane of the plate. An occulting disk 16 issupported for rotation by a bearing supported drive shaft 18 extendedthrough the plate 12 and driven by a drive unit 20. As illustratedparticularly in FIGS. 1 and 3, a counter rotor 22 is coupled with theplate 12 for purposes of balancing reaction torque applied tothe plate12 as the drive unit 20 imparts rotation to the occulting disk 16. Asillustrated in FIG. 1, a camera unit 24 having a filter holder 25 issecured to the plate 12 for purposes of achieving a photographicexposure of light sensitive material contained therewithin.

As a practical matter, the camera unit 24 is of any suitable type,including a plate camera which utilizes a 4-by-5 inch photographicplate, not shown. In such instances, theaperture 14 provides a field ofnot less than 3 inches in diameter. Furthermore, while not illustrated,the shutter has particular utility in conducting photographic operationsutilizing a 24 inch telescope. Consequently, the specific camera cameraunit employed, as well asthe specific structure employed in coupling themounting plate 12 within an operative system is a matter of conveniencedictated by the particular environment in which the camera is to beemployed.

It is, of course, deemed feasible to support the plate 12 in a mannersuch that the counter rotor 22 can be eliminated. However, since theshutter 10 normally is employed in an environment wherein accurateness,predictability of function, and uniformity of exposure is, for practicalpurposes, deemed to be imperative, use of the counter rotor 22 is deemedto be particularly practical. Additionally, vibration induced by theshutter operation shock would blur any short exposure without counterrotation.

Occulting Disk As best illustrated in FIG. 2, the occulting disk 16 is asegmented disk fabricated from a suitable opaque material, such as alightweight metal. The disk includes a first radiation transmittingsector 26 and a second transmitting sector 28 diametrically opposed tothe first sector. The sector 26, in effect, is a wide angle sector,while the second sector, in effect, in a narrow angle sector. Thesesectors are formed by truncating the disk 16 along selected radii and ina manner such that the sectors are symmetric about a common diameter andare related in diametric opposition. Since the disk 16 is formed from anopaque material it can be appreciated disk 16 is divided into a pair oftransmitting sectors of unequal dimensions while the occulting sectorsare of equal dimensions. Sector angles of 80 and 5 are chosen forconvenience. Because exposure times have been arbitrarily selected to bein the ratio of a power of two, the sector angles were also chosen as aratio of 16, Le, 2 to the 4th power. In fact, considerable lattitudeexists in choosing specific sector angles, including the use of only asingle transmitting sector.

It is to be understood that the disk 16 is, in operation, selectivelydriven in a first mode of operation wherein the wide angle radiationtransmitting sector 26 is adthat the transmitting sectors 26 and 28 areseparated by a pair of mutually spaced occulting sectors, includingafirst occulting sector 30 and a second occulting sector 32.

For reasons which can readily be appreciated, the overall dimension ofthe disk 16 and the sectors 26 through 32 is determined by the operativerequirements imposed on the shutter 10. As currently employed, theaperture 14 has a diameter of 3 inches, while the occulting disk has adiameter of 12 inches. Therefore, the radiation transmitting sectors 26and 28 are formed by radially severing the material of the disk 16, frompoints located on its periphery, to a depth of approximately 3 inches.As a practical matter, the side edge surfaces of each of the sectorsaredefined by lines of severance extending along angularly relatedradii.

The wide angle radiation transmitting sector 26 is defined by radiallyextended lines of severance which, when projected to the center of thedisk 16, define therebetween an included angle of 80", Similarly, the

narrow angle radiation transmitting sector 28 is provided betweenradially extended lines of severance which, when projected to the centerof the disk, define therebetween an included angle of 5. Therefore, the

vanced across the aperture 14, for thereby providing a radiation pulseof a relatively long duration and driven in a second mode, for therebyadvancing the sector 28 across the aperture 14 for thus providing apulse of radiation of a relatively short duration. Hence, it can readilybe appreciated that by driving the occulting disk 16 in selected modesat selected rates, a controlled gating of radiation delivered throughthe aperture 14 is achieved for accurately providing selectively pulsedradiation for thus accommodating selectivity in photographic operations.

Due to the inequality in the quantity of the material removed from thediametrically opposed portions of the disk 16, in establishing theradiation transmitting sectors 26 and 28, the occulting disk 16 is bothstatically and dynamically unbalanced. Therefore, a counterweight 34 ofappropriate mass is coupled to the disk 16 through any suitable means,including screws 36. Consequently, both static and dynamic balance isachieved for the disk 16 as it is driven in rotation by the drive unit20.

Drive Unit The drive unit 20, as illustrated in FIG. 3, includes atorque motor 40 operatively mounted within a housing 41. The housingrigidly is coupled to the plate 12 through a bearing collar 42 seatedwithin a circular opening 44 appropriately formed therewithin. Thecollar 42 is coupledto the plate 12 through a multiplicity of mountingscrews 46 extended through suitable openings formed in the plate andthreadably received within the collar 42.

The collar 42 includes a circular opening 48 within which is seated anannular bearing race 50. This bearing race serves to rotatably supportthe drive shaft 18 near its output end 52, to which is coupled the disk16. As a practical matter, the drive shaft 18 is coupled with the disk16 through a plurality of studs threadingly received within the driveshaft, so that as the drive shaft is driven in rotation a responsiverate of rotation is imparted to the occulting disk 16.

The particular motor employed is dictated by the prevailing operativerequirement, such as required rates of angular acceleration to beimparted to the occulting disk 16. Since D.C. motors are well known andare commercially available, a detailed description of the motor employedis omitted in the interest of brevity. However, it is noted that themotor currently utilized in driving the disk 16 is a D.C. motor whichconsumes 75 watts of power in driving the occulting disk to its highestrate of angular velocity of approximately 420 rpm (revolutions perminute) within of angular rotation.

For reasons which readily are apparent, as the motor 40 is energized fordriving the disk 16, the plate 12 experiences an application of reactiontorque. The effect of this torque is countered through an energizationof the counter rotor 22, which serves to apply reaction torque inopposition to the reaction torque applied by the, motor 40. I i

Preferably, the applied reaction torques are of equal magnitudes. Toachieve this condition, the counter rotor 22 is mounted within a housing56 and coupled to the plate 12 through a plurality of screws 58, in amanner similar to that in which the housing 41 is coupled with the plate12. In practice, a housing 56 includes therein a DC. torque motor 60 ofa design and having operative characteristics closely matched to thoseof the motor 40. The motor 60 operatively is coupled with a dummyfly-wheel 62 and is adapted to be reversely rotated thus to act inopposition to the occulting disk 16. However, it particularly is to beunderstood that the dummy fly-wheel 62 is supported by a suitableplurality of bearings 64 arranged within the housing 56 and coupledthereto through a multiplicity of screwthreaded studs 66 in order thatopposed angular momentum be imparted to both the fly-wheel 62 and thedisk 16 as the motors 40 and 60 simultaneously are driven at commonrates, but in opposed directions. Hence, the motors 40 and 60 developand apply oppositely directed reaction torques to the mounting plate 12.This application of opposed and equal torques serves to achieve acancellation of displacement inducing-forces developed in response to anenergization of the motors, as illustrated by the force vector arrows inFIG. 6.

Since the shutter 10 -is employed in gating radiation for photographicpurposes, it'is imperative that only a single pulse of radiation bedelivered through the aperture 14, for each cycle of shutter operation,in order to prevent an occurrence of double exposure of photographicmedium being exposed by the radiation. Therefore, the motor 40 mustaccelerate the occulting disk 16 to an appropriate steady state as oneof the occulting sectors and 32 transverse the opening of the aperture14, and yet achieve a deceleration of the disk 16 to a zero velocitysteady state while the other occulting sector traverses an opening ofthe aperture, subsequent to a passage of a single one of thetransmitting sectors 26 and 28, from before the opening.

As illustrated in FIGS. 4a through 4d, where the gating of radiation isto be achieved employing the wide angle transmitting sector 26,acceleration of the disk 16 is initiated while an. occulting segment 30is coincident with the opening of the aperture 14. The motors 40 and 60simultaneously are energized for imparting clockwise rotation to thedisk 16, as viewed in FIGS. 2 and 4a through 4d. As the disk 16 isrotated from the position illustrated in FIG. 4a to that illustrated inFIG. 4b, it is accelerated from a zero velocity to a steady statevelocity. This, of course, occurs as the occulting sector 30 traversesthe opening of the aperture 14.

Consequently, the angular velocity of the disk 16 is stabilized beforetransmission of radiation through the aperture 14 isinitiated, asdisplacement of the sector 26 across its opening is initiated. As thedisk 16 is driven in its steady state rotation, from the positionillustrated in FIG. 4b to that illustrated in FIG. 40, a gating of apulse radiation is achieved as radiation is delivered through theaperture 14. The width of the pulse is determined by the duration of thedelivery of the radiation, which is terminated as the occulting sector32 is displaced into coincidence with the opening so that iteffectively'covers the aperture 14. At this point, deceleration of thedisk 16 is initiated in order to prevent an overshoot of the sector 32.Such an overshoot would cause the transmitting sector 26. to be broughtinto operative alignment with the aperture 14 and would result intransmission of a second pulse during a single cycle of operation of theshutter 10. Hence, it should readily beapparent that during a singlecycle of shutter operation a fractional turn of asingle revolution of adisk 16 is employed for gating a single pulse of radiation through theaperture. I

In order to achieve a second cycle of operation, following the cycleillustrated in FIGS. 4a through 4d, a reverse direction of rotational isimparted'to the disk 16 for causing the disk to rotate in a counterdirection wherein a progression through the steps illustrated in FIGS.4a through FIGS. 4d is reversed so that a second cycle is completed asthe disk comes to rest in a position, substantially as shown in FIG. 4a.

' Control Circuit In order to control the operation of the motors 40 and60, circuitry similar to that illustrated in FIG. 5 has been provided.

Due to the fact that the disk 16 is, in effect, oscillated in fractionalturns of rotation, for thus causing selected radiation transmittingsectors to traverse the opening 14, the motors 40 and reversely areenergized for the purposes of reversing directions of rotationaldisplacement imposed on the disk. Therefore, for purposes ofillustration, it can be assumed that the motors 40 and 60 are controlledthrough a servo-control circuit 70, which serves to dictate direction ofangular displacement imparted to the disk 16 as the motors 40 and 60 areenergized and to detect and control and operative angular position ofthe disk relative to the aperture Acceleration, steady state angularvelocity, and deceleration are achieved by employing a DC. poweramplifier 72 which simultaneously delivers an integrated output signalto the motors 40 and 60 for driving the motors in a selectable andaccurately controlled manner. The power amplifier 72 is of thecommercially available design which serves to sum three separate inputsignals simultaneously derived from a ramp generator 74, a bank ofshaft-connected potentiometers 76 and a tachometer 78. Since the circuitcomponents herein employed. are of a known design and are commerciallyavailable, a detailed description of the components is omitted in theinterest of brevity. It is, however, to be understood that the rampgenerator 74 serves to provide a ramp output signal of an increasingvoltage, such as that illustrated in FIG. 7. Such a signal is aselectively variable signal which can readily be achieved through aselective operation of ramp signal generators of known design. Inpractice, the output signal derived from the ramp signal generator 74 isutilized as a reference signal indicating a desired angular position forthe disk 16 for each point in time, between points in time designatedT-l and T-2. Therefore, the

voltage level of the signal derived from the ramp generator 74 serves toindicate the appropriate position for the disk 16, at each instant,while the slope of the signal is indicative of the rate of positionchange or the required velocity of the disk 16.

The output bank of potentiometers 76 is employed to provide an outputsignal which is delivered to the power amplifier 72 in order to indicatethe instantaneous position of the disk 16 at any given instant in time.The signal derived from the bank of potentiometers 76 is added to theinput signal derived from the ramp generator 74 and utilized in drivingthe amplifier circuit 72 for acquiring a power output utilized inachieving an appropriate angular position at a given instant in time.

The bank of potentiometers 76 includes a first potentiometer 80 having awiper arm 81 coupled with the output shaft 18 of the motor 40 through asuitable drive shaft 82, FIG. 3. This shaft is coupled with the outputshaft of the motor 40 through a suitable coupling including a bearingcollar 84 mounted on the housing 41 through studs 86. The shaft 82further is coupled to a wiper arm 87 of a second potentiometer 88coaxially aligned with the first potentiometer 80, mounted at eitherside thereof. The potentiometers 80 and I 88 suitably are supportedwithin a housing 90 extended from the housing 41 of the motor 40.

The particular order in which the potentiometers are mounted is a matterof convenience. However, in order to facilitate the coupling of theshaft 82 with the coaxially aligned potentiometers, suitablepin-andsleeve couplings 92 are employed. The potentiometers, therefore,are driven in a manner such that their wiper arms 81 and 87 aredisplaced at a rate and in a direction dictated by the motor 40 as it isdriven to impart displacement to the disk 16.- The potentiometers eachhave 360 of free mechanical rotation but, as a practical matter, only350 of electrical rotation, with the wiper arms thereof being inparallelism with each other and with the axis of symmetry oftransmitting sectors 26 and 28. As illustrated in FIG. 5, thepotentiometers 80 and 88 are aligned 180 apart, with respect to theirelectrical polarity and the relative orientation of. their gaps. Thisarrangement permits the potentiometers to'track the angular position ofeither of the transmitting sectors 26 and 28 of the disk 16 over 350 ofrotation so as to provide an input signal to the power amplifier 72indicative of the tracked position. As a practical matter, thepotentiometers 80 and 88 directly are coupled with a suitable source 94of the DC. voltage, while a switch 96 is provided between the poweramplifier 72 and the potentiometers 80 and 88. Hence, signalsselectively can be derived from either of the potentiometers through theswitch 96, depending upon which sector is being used.

The particular potentiometer selected for a given mode is dictated bythe desired mode of operation to be imposed on the disk 16. For example,where the gating of radiation is to be achieved employing the wide angletransmitting sector 26, the power amplifier 72 is coupled with thepotentiometer 80, as illustrated in FIG. 5. Since the narrow angleradiation transmitting sector 28 is, in effect, diametrically opposed tothe wide angle sector, the arm 87 of the potentiometer 88 is related tothe arm "81 of the potentiometer 80. It is to be understood thatdepending upon the transmitting sector for use in driving the motors 40and 60.

In order to reduce the inherent tendency of the output of the poweramplifier 72 to rapidly vary, due to the continuous summing of thesignals derived from the bank of potentiometers 76 and the rampgenerator 74, a damping voltage signal is acquired from the tachometer78, which is coupled with the motor 40 in tandem and driven by itsoutput shaft 18, FIG. 3. The output of the tachometer 78 is proportionalto the rate of the rotation imparted to the shaft 18 and is applied tothe amplified 72 in a manner such as to damp out variation in thevoltage levels of the signals applied to the motors 40 and 60. Thesevariations result from variations occurring in potentiometer position asthe position of the motor shaft attempts to follow the output signalderived from the ramp generator. The use of tachometer derived dampingsignals for second order positional servo systems is well known and isdescribed in detail in numerous texts on the subject.

' Since such damping techniques are well within the skill of the art andform no specific part of the instant invention, a detailed descriptionis omitted in the interest of brevity. Therefore, it is to be understoodthat the servo-control circuit is, in effect, a position servo-system,wherein the angular acceleration imposed on the disk 16 is, at itsvarious positions relative to the aperture 14, dictated by a signalderived from the ramp generator 74, summed with the signal derived fromthe potentiometer and the signal derived from the tachometer.

In certain instances, it may be found desirable to provide exposureintervals of excessive duration. This is achieved by gating theradiation in a manner such that the resulting pulses are of a widthcommensurate with a desired interval. This can be achieved simply bystepping the disk 16 in a manner such as to present the opening of theaperture 14 to a selected source of radiation for a predeterminedperiod. This stepping mode can be achieved by driving the ramp generator74 in a manner such as to acquire an output signal of a shape such asthat illustrated in FIG. 8. Wherein a constant voltage condition isimposed on the motors 40 and 60 for a given period of time extendingbetween T-l and T-2.

OPERATION It is believed that in view of the foregoing description, theoperation of the shutter will be readily understood and it will bebriefly reviewed at this point. The shutter 10 is, in practice,associated with a camera unit 24 and aligned in a manner consistent withthe intended use of the camera. With the camera unit 24 and shutter 10thus positioned and aligned, a selection of a wide angle or a narrowangle transmitting sector is made with occulting sectors 30 and 32 beingexposed in a radiation blocking relationship to the opening of theaperture 14.

Assuming that the radiation to be gated is to be delivered in relativelywide pulses, the switch 96 is coupled with the potentiometer 80, asillustrated in FIG. 5, and the occulting disk 16 is positioned in amanner condelivered from the ramp generator 74 for providing a signalindicative of the instantaneous position change required in order toachieve a steady state of. rotation for the disk 16. No later than theinstant at which the occulting disk 16 is rotated to position theocculting sector 30 of the disk 16 in a position indicated in FIG. 4b,,a steady state of angular velocity is established for the disk 16. Asthe transmitting sector 26 traverses the aperture 14, at a steadyanduniform rate, radiation is delivered through the aperture 14 to providea uniform pulse of radiation in order to achieve a photographic exposurewithin the camera unit 24.

Depending upon the lapse of time required by the sector 26 in traversingthe opening of the aperture 14, an exposure interval of a predeterminedlength is established as gating of the radiation occurs by the passageof the sector 26. Once the transmitting sector 26 has traversed theopening of the aperture 14 deceleration of the disk 16 is initiated, asthe occulting sector 32 covers the opening of the aperture for thusterminating the pulse.

Due to the reaction torque applied to the plate 12, as the motor 40 isenergized, the plate 12 necessarily tends to rotate about an axis ofrotation. However, due

.to the fact that the motor 60 concurrently is energized and is drivenin a direction opposite to the direction of the motor 40, for purposesof driving the dummy flywheel 62, a reverse reaction torque is appliedto the plate 12. The two forces tend to achieve mutual cancellation androtation of the plate is avoided.

ln the event that exposure is to be achieved over a relatively shortperiod of time, the narrow angle transmitting sector 28 is prepared tobe driven across the aperture 14. This is achieved in a manner similarto that hereinbefore described with respect to the wide angle radiationtransmitting sector 26. In this instance, however, the switch 96 iscaused to close a circuit between the potentiometer 88 and the poweramplifier 72. A cycle of operation then is achieved in a manner similarto that described with respect to the gating of radiation employing thewide angle transmitting sector 26. When a pulse of a large width isrequired, the ramp generator 74 is driven to provide an output. signalsimilar to that illustrated in FIG. 8 whereby the transmitting segmentis caused to traverse the opening of the aperture 14 at very low butconstant rates.

With the system assembled in the manner hereinbefore described, it is tobe understood that the disclosed embodiment of the instant inventionprovides an optical shutter 10 which accurately, reproducibly and withbetter than one percent uniformity, transmits pulsed radiation through a3 inch diameter aperture for a wide range of selectable time intervals,ranging between one-five-hundred-and-twelfth second, to pulses of verylarge pulse widths including 32 seconds, while the occulting disk 16 isdriven through less than a single turn of rotation.

The disk 16 is capable of obtaining a constant, but selectivelyvariable, angular velocity of approximately 420 rpm, with a precision ofplus or minus one percent, in about of angular displacement. Byselectively reducing the output of the ramp generator 74 in binarysteps, the narrow angle radiation transmitting sector 28 can produceincreasing exposure intervals between one-five-hundred-twelfth secondand on e-sixty-fourth second, while the wide angle radiationtransmitting sector 28 can produce exposure pulses ranging betweenone-thirty-second second to one-fourth second. Of course, when employingthe shutter 10 in a stepping mode, the shutter can be caused to gate theradiation pulses to provide pulses of arbitrary widths up to 4 seconds.

In view of the foregoing, it is readily apparent that the aforedescribedembodiment of the'instant invention provides a simplified, improved andpractical optical shutter for use in photographic operations requiringlarge formats and accurately controlled radiation gatmg.

Although the invention has been herein shown and described in what isconceived to be the most practical and preferred embodiment, it isrecognized that departures maybe made therefrom within the scope of theinvention, which is not to be limited to the illustrative detailsdisclosed.

What is claimed is:

1. A cyclically operable optical shutter comprising:

A. means defining a radiation transmitting aperture having an opticsaxis;

B. an occulting disk including means defining therein a pair ofradiation occulting sectors and a radiation transmitting sectorinterposed between the occulting sectors;

C. means abaxially related to said aperture supporting said disk foroscillatory rotation in a plane disposed in close proximity to saidaperture and normally related to said optics axis, whereby said sectorssequentially are caused to traverse the aperture as the disk is drivenin oscillatory rotation;

D. cyclically energizable means coupled with said disk for angularlyaccelerating the disk from zero velocity to a selected steady-stateangular velocity,

as a first occulting sector is caused to traverse said aperture,maintaining said steady-state angular velocity for said disk as theradiation transmitting sector traverses said aperture, and thereafterdecelerating said disk to a zero velocity as a second occulting sectoris caused to traverse said aperture, whereby during each cycle ofoperation a radiation transmitting sector is caused to traverse saidaperture at a constant velocity for providing a pulse of radiationhaving an accurately predictable width; and

. a counter rotor operatively coupled with said support means forapplying thereto reaction torque in a direction and with a magnitudesufficient for countering reaction torque responsively applied to thesupport as a consequence of the oscillatory rotation imparted to saiddisk.

2. The shutter of claim 1 wherein the disk further includes meansdefining another radiation transmitting sector interposed between saidpair of radiation occulting sectors in diametric opposition to the firstmentioned radiation transmitting sector.

3. The shutter of claim 2 wherein said occulting sectors are defined bycircumscribing surfaces of equal dimensions while said transmittingsectors are defined by surfaces of unequal dimensions.

4. The shutter of claim 2 wherein said transmitting sectorscomprisetruncated portions of the occulting disk. I

5. The shutter of claim 3 wherein one of said sectors is defined betweensurfaces having a projected included angle of 80 while the othertransmitting sector is defined between surfaces having a projectedincluded angle of 5 for thereby providing a wide and a narrow radiationtransmitting sector.

6. An optical shutter comprising:

A. a mounting plate;

B. a means defining an aperture in the mounting plate;

C. an occulting disk including a pair of diametrically related,radiation transmitting sectors and a pair of occulting sectorsinterposed between the radiation transmitting sectors;

D. means mounting said disk on said mounting plate for rotation in aplane parallel to the plane of the aperture and in a manner such thatthe transmitting sectors and the occulting sectors alternately traversesaid aperture as the disk is rotated, whereby pulsed radiation is gatedthrough said aperture;

E. drive means including an electrically energizable motor coupled withsaid occulting disk for imparting selected fractional turns of rotationto said disk;

F. control means coupled with said drive means including a rampgenerator for providing a reference signal indicative of selectedinstantaneous angular dispositions to be imposed on said disk asrotation is imparted thereto;

G. a bank of potentiometers including means for delivering an outputsignal indicative of instantaneous angular dispositions imposed on thedisk as it is driven in rotation;

H. a DC. power amplifier coupled with said ramp generator and said bankof potentiometers for receiving and electrically summing signalsdelivered thereto from the ramp generator and said bank potentiometersand for delivering an output voltage to said drive means for causingsaid drive means to correct position error operationally establishedbetween the instantaneous angular dispositions imposed on said disk andthe selected instantaneous dispositions to be imposed on said disk; and

I. a tachometer coupled with said drive means and said power amplifierfor delivering a damping voltage to said power amplifier.

7. The shutter of claim 6 wherein means including a counter-rotoroperatively is coupled with said mounting plate for cancelling reactiontorque developed and apglied to said mounting plate by said drive means.

. The shutter of claim 7 wherein said counter-rotor includes a motor andan operatively associated dummy fly-wheel driven simultaneously inopposition to said disk and at rates coincident therewith.

1. A cyclically operable optical shutter comprising: A. means defining aradiation transmitting aperture having an optics axis; B. an occultingdisk including means defining therein a pair of radiation occultingsectors and a radiation transmitting sector interposed between theocculting sectors; C. means abaxially related to said aperturesupporting said disk for oscillatory rotation in a plane disposed inclose proximity to said aperture and normally related to said opticsaxis, whereby said sectors sequentially are caused to traverse theaperture as the disk is driven in oscillatory rotation; D. cyclicallyenergizable means coupled with said disk for angularly accelerating thedisk from zero velocity to a selected steady-state angular velocity, asa first occulting sector is caused to traverse said aperture,maintaining said steady-state angular velocity for said disk as theradiation transmitting sector traverses said aperture, and thereafterdecelerating said disk to a zero velocity as a second occulting sectoris caused to traverse said aperture, whereby during each cycle ofoperation a radiation transmitting sector is caused to traverse saidaperture at a constant velocity for providing a pulse of radiationhaving an accurately predictable width; and E. a counter rotoroperatively coupled with said support means for applying theretoreaction torque in a direction and with a magnitude sufficient forcountering reaction torque responsively applied to the support as aconsequence of the oscillatory rotation imparted to said disk.
 2. Theshutter of claim 1 wherein the disk further includes means defininganother radiation transmitting sector interposed between said pair ofradiation occulting sectors in diametric opposition to the firstmentioned radiation transmitting sector.
 3. The shutter of claim 2wherein said occulting sectors are defined by circumscribing surfaces ofequal dimensions while said transmitting sectors are defined by surfacesof unequal dimensions.
 4. The shutter of claim 2 wherein saidtransmitting sectors comprise truncated portions of the occulting disk.5. The shutter of claim 3 wherein one of said sectors is defined betweensurfaces having a projected included angle of 80* while the othertransmitting sector is defined between surfaces having a projectedincluded angle of 5* for thereby providing a wide and a narrow radiationtransmitting sector.
 6. An optical shutter comprising: A. a mountingplate; B. a means defining an aperture in the mounting plate; C. anocculting disk including a pair of diametrically related, radiationtransmitting sectors and a pair of occulting sectors interposed betweenthe radiation transmitting sectors; D. means mounting said disk on saidmouNting plate for rotation in a plane parallel to the plane of theaperture and in a manner such that the transmitting sectors and theocculting sectors alternately traverse said aperture as the disk isrotated, whereby pulsed radiation is gated through said aperture; E.drive means including an electrically energizable motor coupled withsaid occulting disk for imparting selected fractional turns of rotationto said disk; F. control means coupled with said drive means including aramp generator for providing a reference signal indicative of selectedinstantaneous angular dispositions to be imposed on said disk asrotation is imparted thereto; G. a bank of potentiometers includingmeans for delivering an output signal indicative of instantaneousangular dispositions imposed on the disk as it is driven in rotation; H.a D.C. power amplifier coupled with said ramp generator and said bank ofpotentiometers for receiving and electrically summing signals deliveredthereto from the ramp generator and said bank potentiometers and fordelivering an output voltage to said drive means for causing said drivemeans to correct position error operationally established between theinstantaneous angular dispositions imposed on said disk and the selectedinstantaneous dispositions to be imposed on said disk; and I. atachometer coupled with said drive means and said power amplifier fordelivering a damping voltage to said power amplifier.
 7. The shutter ofclaim 6 wherein means including a counter-rotor operatively is coupledwith said mounting plate for cancelling reaction torque developed andapplied to said mounting plate by said drive means.
 8. The shutter ofclaim 7 wherein said counter-rotor includes a motor and an operativelyassociated dummy fly-wheel driven simultaneously in opposition to saiddisk and at rates coincident therewith.